Block paving over concrete

[David 1234]

I have a 90 square meter driveway of block paving that has been down for over 20 years on top of a 100mm think slab of concrete. The driveway isn't too bad considering its age but there are indentations where cars regularly park.

It's time to have a new driveway and I can see that its inadvisable to have a flexible construction over rigid concrete, but it seems a pity to break up a perfectly good large slab of concrete. I have lifted a few blocks and the pavers have been laid on sand so I am guessing that that the reason there are indentations is a lack of drainage.

A contractor has suggested that there will not be a problem with taking up the old pavers and laying new ones again on sand, but then sealing so that water runs off this time and doesn't sit under the paving above the concrete causing the same problem again.

Is this a sound solution and if not how about laying the blocks with mortar as detailed on this site? I am really trying to avoid breaking up the old concrete pad, disposing of it and bringing in tons of type 1.

[Pablo]

Fin drains will do your job nicely sealant won't because it will not remain impervious to water. A fin drain is basically and blanket of two layers that allows the water to flow between them whilst taking the weight of the finished surface. They're very thin and won't cause any problems with levels.

[Mikey_C]

I am really trying to avoid breaking up the old concrete pad, disposing of it and bringing in tons of type 1.

you could break up the pad, crush it on site with a smaller crusher and use it as type 1. (still not probably what you are ideally looking for, but a solution).

have you considered tarmac, resin bound aggregate or pic on top of the already solid concrete, if depth allows.

[seanandruby]

read me As long as the base is sound and meets the above standards, then it will be ok. Also put in place a linear drain, or simular.

[David 1234]

Thank you all for your advice. Pablo I've read the section on fin drains. I found it a bit confusing as it didn't show the use of fin drains in a driveway. Can you tell me please how these would be laid in a driveway and am I right to assume that if I went down the rigid route then fin drains would no longer be relevant and I could simply rely on a fall and linear drainage?

Oh and thanks Mikey but I think block paving is what I'm after - the PIC I've seen doesn't do it for me.

[GB_Groundworks]

If I remebet correctly last time this was discussed holes drilled at 600 centres and geotextile to prevent sand filling them up was the gaffers answer. I asked about punching the holes with a pecker that's why I remember it.

[mickg]

the correct way is to drill 50mm holes in the concrete at no more than 1 metre centres, fill each hole with MOT type 1 and compact, lay a geotextile layer over the total area so the sand laying course can't migrate in the MOT

continue to lay the sand laying course to the total area and compact using a vibrating plate, screed the sand to the correct level and fall to disperse any surface water and lay the block paving to your chosen pattern or design

[David 1234]

Thank you both. Is the MOT permeable enough to act as a drain in this situation and is this an alternative to fin drains or kind of a home made fin drain?

[GB_Groundworks]

you could use a 6/10/20mm washed aggregate if you wanted to be extra careful

but thats the best way to do it as mick has said

[mickg]

yes it is permeable enough as your not going to get totally compacted hardcore in a 50mm hole when its been compacted using a lump hammer or similar manual method

what ever you do don't try using a vibrating plate to compact the hard core into the holes on top of the concrete as you will find it will be bouncing all over the place and is dangerous

the idea of the holes in the concrete is for drainage to relieve any water pressure that may build up within the sand laying course, in your case the blocks have sunk slightly where the car is parked but in other situations the blocks have been pushed up

[seanandruby]

I would of thought because it is an existing driveway being upgraded that the permeable act would'nt apply and to drain where it has been draining to, ie surface water drain? correct me if i'm wrong. Seems a shame to break up a perfectly good concrete slab.

[GB_Groundworks]

its not about the planning issue sean, its to prevent a puddling in the sand laying corse which is on the impermeable concrete, which can cause puddling and as mick says floating blocks from the hydraulic pressure

[seanandruby]

But you would'nt use sand only, on a concrete base. Would you ???
It's either, rigid, or flexible, one, or t'other. If you are drilling holes in an existing base then i would of thought a no fines 10ml concrete would be the bedding. Either that, or, as was stated...."rip it out and start again". It's a bit of an oxymoran really.

[mickg]

actually Marshall's technical department do advise the way I have described, I phoned last year and got the specification as above

but your right in what your saying sean as I do lay driveways using the rigid method if the ground conditions require it but to give that advice on the forum could lead to problems because if your not very clean and careful you will have semi dry mixture all over the face of the block paving and kerbs leading to cement staining

[seanandruby]

some people are " clean and careful". If they ask for advice on something, then don't we then give them that advice. We can only go so far the rest is up to them, ie being " clean and careful?" I;m not being pedantic mick, i'm just curious